Conventionally, a cordierite honeycomb structure with a catalyst loaded therein is used for treating toxic substances contained in an exhaust gas emitted from an automobile engine. Use of a honeycomb structure formed from a silicon carbide sintered body for purification of the exhaust gas is also known (see, for example, Patent Document 1).
When exhaust gas is treated by the catalyst loaded in the honeycomb structure, the catalyst needs to be heated to a predetermined temperature. At the starting up of the engine, however, the catalyst temperature is low, and therefore there is a problem that the exhaust gas is not sufficiently purified.
To deal with this, a metallic heater is provided upstream of the honeycomb structure with the catalyst loaded therein, in order to elevate the exhaust gas temperature (see, for example, Patent Document 2).
There is also disclosed use of another honeycomb structure, which is provided with electrodes at both ends thereof and is made from conductive ceramics as a heater-attached catalyst carrier (see, for example, Patent Document 3). Still another ceramic honeycomb structure that has electrodes on its side face and generates heat upon application of electricity is disclosed (see, for example, Patent Document 4).